The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Known internal combustion engines configured to operate lean of stoichiometry may be equipped with exhaust aftertreatment systems including three-way catalytic converters and ammonia-selective catalytic reduction (NH3-SCR) catalysts to treat constituents in an exhaust gas feedstream. Such known systems generate and store ammonia on a catalytic surface of the NH3-SCR catalyst to react with exhaust gases. Ammonia may be generated by passing a rich exhaust gas feedstream through a three-way catalytic converter upstream of an NH3-SCR catalyst under specific engine operating conditions. The stored ammonia reduces nitrogen oxide (NOx) molecules in the exhaust gas feedstream to elemental nitrogen and water under a range of operating conditions associated with temperature and flowrate. Stored ammonia may separate from a NH3-SCR catalyst and pass into the exhaust gas feedstream under specific operating conditions. This is referred as ammonia slip.
Known internal combustion engines execute partial or complete fuel cutoff during vehicle deceleration events when an operator torque request is less than a threshold, with or without the engine continuing to rotate. Such operation reduces and changes flow of exhaust gas constituents to an exhaust aftertreatment system, which may cause decreased temperatures and associated reduced conversion efficiency in the exhaust aftertreatment system. During subsequent engine operation, engine control schemes may be required to operate at non-optimum fueling and operating points to increase conversion efficiency.